package com.mxc.split.util;

/**
 * 描述: Twitter的分布式自增ID雪花算法snowflake (Java版)
 *
 * @author yanpenglei
 * @create 2018-03-13 12:37
 **/
public class SnowFlake {

	/**
	 * 起始的时间戳
	 */
	private final static long START_STMP = 1480166465631L;

	/**
	 * 每一部分占用的位数
	 */
	private final static long SEQUENCE_BIT = 12; // 序列号占用的位数
	private final static long MACHINE_BIT = 5; // 机器标识占用的位数
	private final static long DATACENTER_BIT = 5;// 数据中心占用的位数

	/**
	 * 每一部分的最大值
	 */
	private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
	private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
	private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

	/**
	 * 每一部分向左的位移
	 */
	private final static long MACHINE_LEFT = SEQUENCE_BIT;
	private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
	private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

	private long datacenterId; // 数据中心
	private long machineId; // 机器标识
	private long sequence = 0L; // 序列号
	private long lastStmp = -1L;// 上一次时间戳

	public SnowFlake(long datacenterId, long machineId) {
		if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
			throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
		}
		if (machineId > MAX_MACHINE_NUM || machineId < 0) {
			throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
		}
		this.datacenterId = datacenterId;
		this.machineId = machineId;
	}

	/**
	 * 产生下一个ID
	 *
	 * @param ifEvenNum 是否偶数 true 时间不连续全是偶数 时间连续 奇数偶数 false 时间不连续 奇偶都有
	 * @return
	 */
	public synchronized long nextId(boolean ifEvenNum) {
		long currStmp = getNewstmp();
		if (currStmp < lastStmp) {
			throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
		}
		/**
		 * 时间不连续出来全是偶数
		 */
		if (ifEvenNum) {
			if (currStmp == lastStmp) {
				// 相同毫秒内，序列号自增
				sequence = (sequence + 1) & MAX_SEQUENCE;
				// 同一毫秒的序列数已经达到最大
				if (sequence == 0L) {
					currStmp = getNextMill();
				}
			} else {
				// 不同毫秒内，序列号置为0
				sequence = 0L;
			}
		} else {
			// 相同毫秒内，序列号自增
			sequence = (sequence + 1) & MAX_SEQUENCE;
		}

		lastStmp = currStmp;

		return (currStmp - START_STMP) << TIMESTMP_LEFT // 时间戳部分
				| datacenterId << DATACENTER_LEFT // 数据中心部分
				| machineId << MACHINE_LEFT // 机器标识部分
				| sequence; // 序列号部分
	}

	private long getNextMill() {
		long mill = getNewstmp();
		while (mill <= lastStmp) {
			mill = getNewstmp();
		}
		return mill;
	}

	private long getNewstmp() {
		return System.currentTimeMillis();
	}

	public static void main(String[] args) throws Exception {
		/**
		 * 分布式数据中心id 机器id
		 */
		SnowFlake snowFlake = new SnowFlake(5, 6);
		for (int i = 0; i < 10; i++) {
			/**
			 * 时间连续 奇数偶数都有
			 */
			// System.out.println(snowFlake.nextId(true));
			/**
			 * 429407369643581440 429407369643581441 429407369643581442 429407369643581443
			 * 429407369643581444 429407369643581445 429407369643581446 429407369643581447
			 * 429407369643581448 429407369643581449
			 */
			// System.out.println(snowFlake.nextId(true));
			/**
			 * 时间不连续 原版 获取的id全是偶数
			 */
			// Thread.sleep(1);
			/**
			 * 429407954194935808 429407954199130112 429407954207518720 429407954211713024
			 * 429407954215907328 429407954224295936 429407954249461760 429407954253656064
			 * 429407954257850368 429407954262044672
			 */
			long snowFlakeId = snowFlake.nextId(false);
			System.out.println(snowFlakeId);
			/**
			 * 时间不连续 改版 获取的id为奇偶数
			 */
			Thread.sleep(1);
			/**
			 * 429408617683496961 429408617691885570 429408617696079875 429408617700274180
			 * 429408617704468485 429408617708662790 429408617712857095 429408617717051400
			 * 429408617725440009 429408617729634314
			 */

		}
	}
}